my BMW 3 Series E90/E91 (2005-2012) has a P0171 code, what does that mean?

Solution

1. Preparation

• Gather the necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool before beginning work.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines and intake manifold gaskets for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner to detect leaks around the intake manifold and hoses.
  3. Replace any damaged hoses or gaskets as necessary.
• Tools Required: Smoke machine, carburetor cleaner, basic hand tools.

3. Clean or Replace Mass Airflow Sensor (MAF)

• Sub-steps:
  1. Locate the MAF sensor, usually found between the air filter and the throttle body.
  2. Disconnect the electrical connector and remove the MAF sensor from the intake duct.
  3. Clean the sensor with MAF cleaner spray; do not touch the sensor elements.
  4. Reinstall the MAF sensor and reconnect the electrical connector.
• Tools Required: MAF cleaner spray, screwdriver.

4. Check Fuel Pressure

• Sub-steps:
  1. Attach a fuel pressure gauge to the fuel rail test port.
  2. Turn the ignition to the "ON" position (do not start the engine) and observe the pressure reading.
  3. Compare the reading to the manufacturer's specifications; replace the fuel pump or filter if pressure is low.
• Tools Required: Fuel pressure gauge.

5. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail with injectors attached.
  2. Inspect the injectors for clogs or debris.
  3. If necessary, clean injectors using an ultrasonic cleaner or replace them.
  4. Reassemble the fuel rail and reconnect it to the engine.
• Tools Required: Fuel injector cleaner, basic hand tools.

6. Test Oxygen Sensor

• Sub-steps:
  1. Locate the upstream oxygen sensor on the exhaust manifold.
  2. Disconnect the sensor and connect a multimeter to its terminals.
  3. Start the engine and monitor the voltage; it should fluctuate between 0.1V and 0.9V.
  4. Replace the oxygen sensor if it shows a constant voltage or is outside specified range.
• Tools Required: Multimeter, oxygen sensor socket.